long arm vs. short arm

[PapaPump]

Ford TTB is not a dual wishbone setup. yes is is independent and therefore unrelated to stock cherokee suspension other than it has coils. when you convert your cherokee to long arm, in most cases you are converting to a radius arm setup and that is where the comparison is. the TTB is two lateral arms with one pivot point each, that move in an arc. that much is very different. when viewed from the side though, those arms are located by a radius arm, just like the long arm cherokee setups. when the axle moves up and down, it is forced to move backwards, thus changing castor. when viewed from the side ford TTBs exhibit this same characteristic. so they are similar in that there is a lot of castor change during suspension cycling. (TTB and long arm Cherokee)

 

[cj7xjmj]

I am personally mixed on this question... with the SA kits you are kinda limited to how high you can go... I am running RE DB and rusty's 6.5 coils on my mj. We ahve a couple of guys in the club running LA and they ride nicer on the road, but to me don't seem to flex as well off. Yes you do lose some ground clearance with both kits.. so I guess it is all about how much cash you want to spend on your rig.



Patrick

 

[Double Down]

Dan,

Can you send some pics or post some pics of this so I can get an idea of what you did?

[email protected]

Thanks,

Chris (Double Down)

 

[TrailHunter]

Someone asked about unloading. Unloading is when the front of the rig floats up on steep climbs due to weight transfer, leaving the front with much less traction and putting the rig in an unstable position. One reason long arms tend to increase unloading is that the weight of the front axle/tires/wheels is working (think pulling down) on the rig at a point further back on the frame. Obviously, the further forward weight is distributed the more it will pull down on the front of the vehicle, and more weight forward is better on steep climbs. Since the weight of the front axle assembly is tranfserred to the body through the control arm mounts to the frame, the further back the mounts are the less effect the front axle weight has to work/pull down on the front of the rig. Of course, if the shocks are fully extended the weight will transfer through the shocks, but if you're nose is pointing upward and the shocks are fully extended you are already feeling the effects of unloading. A limiting strap can be used to transfer the weight of the axle assembly to the body at a much more forward location, and limiting straps work well to decrease unloading and to increase steep climbing ability.

I have been searching and seaching for an good explanation for many people's about how long arms by themselves promote uphill unloading and this is it. However I think you're oversimplifying it a lot. Before I get the knee jerk flaming, can we first agree that designing suspension geomtries is not trivial and not black and white. If it where, every single comp buggy and every single stock car in Nascar would run the same setups. The problem I have is how torque is transfered into the frame through the control arms and this is related to anti-squat and dive.

What is anti-squat/dive? It happens when you're on the gas, rotational torque from the axle is transfered into the frame causing it to stay level or even lift depending on how much there is. Whether or not this is really good for you, is a whole other discussion. I've seen this go 20+ pages on pirate with no real answer. So the next question is, how do you create anti-squat/dive? I know with a 4-link, if the upper and lower links are parallel, you have zero 'ant-' characteristics. When the links are closer together at the frame then at the axle, you create the anti-squat/dive characterisitics. Depending on how close they are on the frame depends on how much you get. While I'm not sure with radius arms, you essentially have the the upper and lower control arms mounted together at the frame and wide at the axle which creates as much anit-dive as possible. On flat ground, this isn't really bad because it will keep it level during braking which also causes similar forces. Going uphill as more weight transfers to the rear, the anti-dive characteristics can actually lift the front end. It's not really unloading.

I would have to say that a properly designed front four-link setup, one with equal length links that are parallel, will not have this negative uphill characteristics. I think the link geometries and configuration play a greater roll than where along the vehicle they mount. If longarms where inherintly bad, then why do most if not all rock buggies use them? And by long I mean approximately 30+ inches.

 

[hadAjeep]

Well it doesn't really matter to me now anyway. A few days after my last post the guy I was going to buy the XJ from backed out on me and I never got it. Then the wife changed her mind on me even getting a jeep. Since we already have 2 trucks and 2 cars, all my choice, she decided she gets to pick the next car. So of course I suggested the new HEMI grand cherokee, " or not" was her reply.
Guess I'll just have to abuse my 174" wheelbase dodge ram on jeep trails until I get my jeep. Thanks for all the info.

 

[MaXJohnson]

... I think you're oversimplifying it a lot...

...If longarms where inherintly bad, then why do most if not all rock buggies use them?

Guess we'll have to wait for you to finish reading those 20 pages on PBB and get a handle on this before we'll be seeing the less simplistic explanation.

 

[Spanky414]

Well it doesn't really matter to me now anyway. A few days after my last post the guy I was going to buy the XJ from backed out on me and I never got it. Then the wife changed her mind on me even getting a jeep. Since we already have 2 trucks and 2 cars, all my choice, she decided she gets to pick the next car. So of course I suggested the new HEMI grand cherokee, " or not" was her reply.
Guess I'll just have to abuse my 174" wheelbase dodge ram on jeep trails until I get my jeep. Thanks for all the info.

Easy, sell one of those cars or trucks.

 

[MaXJohnson]

probably have to sell two so he can buy the Jeep and the parts Jeep.

 

[TrailHunter]

Guess we'll have to wait for you to finish reading those 20 pages on PBB and get a handle on this before we'll be seeing the less simplistic explanation.

No need to argue with that. You're right and I'm wrong. :read:

For anyone else that is interested in learning something beyond the piles of opinion being shoveled around, the statement "long arms unload going uphill" is not a completely true statement. It's more correct to say that long arms with a lot of anti-dive will unload going uphill. Since most XJ long arm kits are radius arm style which has a lot of anti-dive, they will unload more than your stock short arms that have good geometry. Well designed 4-link long arm setup will not have the negative characteristics everyone fears.

 

[MaXJohnson]

No need to argue with that. You're right and I'm wrong. :read:

For anyone else that is interested in learning something beyond the piles of opinion being shoveled around, the statement "long arms unload going uphill" is not a completely true statement. It's more correct to say that long arms with a lot of anti-dive will unload going uphill. Since most XJ long arm kits are radius arm style which has a lot of anti-dive, they will unload more than your stock short arms that have good geometry. Well designed 4-link long arm setup will not have the negative characteristics everyone fears.

The term "long arm" as used on this forum and the XJ community in general is synonymous with radius arm. They are essentially the same thing. 4-link designs with long links are not typically referred to as "long arm", they are simply 4-links.

On a lifted XJ, the typical long arm design has less anti-dive than the 4-link it replaces. You would need to have an extreme case of very little lift and drop brackets for this to not be true. If you are aware of a workable 4-link long arm setup that is an exception to this, lets see it. Control of pinion movement is one battle you will be fighting.

I don't see where you have a problem with Richard's "unloading" comment. If you are going uphill, weight will transfer to the rear wheels. Every pound added to the rear wheels is a pound "unloaded" from the front wheels. The lack of anti- forces available to the typical long arm design vs the typical 4-link restrict the front axles ability to control weight transfer.

 

[xjcrawlr]

Here's your answer; www.rockkrawler.com

long-arm (30in), 3 link, antidive/squat worked out very well.

 

[xjcrawlr]

I don't see where you have a problem with Richard's "unloading" comment. If you are going uphill, weight will transfer to the rear wheels. Every pound added to the rear wheels is a pound "unloaded" from the front wheels. The lack of anti- forces available to the typical long arm design vs the typical 4-link restrict the front axles ability to control weight transfer.

Have you given any thought as to what the rear leaves are doing while climbing and that can also affect the weight transfer? Weather or not someone is using a traction bar also plays a role in how weight/force is transfered.

 

[TrailHunter]

The term "long arm" as used on this forum and the XJ community in general is synonymous with radius arm. They are essentially the same thing. 4-link designs with long links are not typically referred to as "long arm", they are simply 4-links.

In my opinion this generalization needs to change. You're basically saying the Full-traction and RockKrawler doesn't make long arm kits because they aren't using a radius arm design.

On a lifted XJ, the typical long arm design has less anti-dive than the 4-link it replaces. You would need to have an extreme case of very little lift and drop brackets for this to not be true. If you are aware of a workable 4-link long arm setup that is an exception to this, lets see it. Control of pinion movement is one battle you will be fighting.

I really am not following you on this one. I just explained in great detail why having radius arms have a lot more anti-dive compared to a 4-link where the upper and lowers are parallel no matter if it the links are short or long.
What kind of pinion movement are you worried about controlling? That caused by a radius arm or 4link?

I don't see where you have a problem with Richard's "unloading" comment. If you are going uphill, weight will transfer to the rear wheels. Every pound added to the rear wheels is a pound "unloaded" from the front wheels. The lack of anti- forces available to the typical long arm design vs the typical 4-link restrict the front axles ability to control weight transfer.

I don't have a problem with his explanation of what unloading is. I have a problem with people assuming long arms cause this to happen more than short arms. Yes moving uphill does transfer weight to the rear. Weight transfer is not affected by the anti- forces created by your suspension. Weight transfer has to do with speed and the the angle of the incline.
You're suspension controls how the torque is applied to the ground. Some say anti- forces are good because it will keep the vehicle flatter thus giving you more control, but others argue it causes a lot of wheel hop and therefore you loose traction. This is what people can't really agree upon. The length of the control arms does not matter, it's their configuration that affects how they handle.

 

[MaXJohnson]

Have you given any thought as to what the rear leaves are doing while climbing and that can also affect the weight transfer? Weather or not someone is using a traction bar also plays a role in how weight/force is transfered.

If you look at the formula for weight transfer, it does not take suspension design into consideration. It is a functin of CG height and acceleration. The design of the rear suspension will determine how much of the weight transfer is carried by the springs vs how much is carried by the suspension links. This does not have an impact on a comparison of longarm vs 4-link, or 3-link for that matter. Either type of front suspension should be compared equally against a common rear suspension or weight transfer model.

I used your link to RockCrawler, but with only a few minutes to spare, didn't see anything related to anti-squat or dive. I'll take a longer look later this evening. Thanks.

 

[MaXJohnson]

Here's your answer; www.rockkrawler.com

long-arm (30in), 3 link, antidive/squat worked out very well.

Help me out Jason. I'm not seeing anything on their site regarding anti-anything.

On the other hand, I have to wonder where they pulled out the strength numbers for their "competitors" steel.

 

[MaXJohnson]

In my opinion this generalization needs to change. You're basically saying the Full-traction and RockKrawler doesn't make long arm kits because they aren't using a radius arm design.

I'm basically saying "The term "long arm" as used on this forum and the XJ community in general is synonymous with radius arm. They are essentially the same thing. 4-link designs with long links are not typically referred to as "long arm", they are simply 4-links."

I really am not following you on this one...

I noticed that too

I don't have a problem with his explanation of what unloading is. I have a problem with people assuming long arms cause this to happen more than short arms.

That anti-dive at the front axle becomes anti-lift when the front axle is under power. This puts the long-arm, with a lower percentage of anti-pitch (new one for ya) at a disadvantage.

cheers

 

[Goatman]

I have been searching and seaching for an good explanation for many people's about how long arms by themselves promote uphill unloading and this is it.

However I think you're oversimplifying it a lot.

For anyone else that is interested in learning something beyond the piles of opinion being shoveled around, the statement "long arms unload going uphill" is not a completely true statement.

I don't have a problem with his explanation of what unloading is.

I have a problem with people assuming long arms cause this to happen more than short arms. Yes moving uphill does transfer weight to the rear. Weight transfer is not affected by the anti- forces created by your suspension. Weight transfer has to do with speed and the the angle of the incline.
You're suspension controls how the torque is applied to the ground. Some say anti- forces are good because it will keep the vehicle flatter thus giving you more control, but others argue it causes a lot of wheel hop and therefore you loose traction. This is what people can't really agree upon. The length of the control arms does not matter, it's their configuration that affects how they handle.

Does anyone get what he is saying? I guess I have to remember that most people use this site for recreation. A good discussion sometimes is an end in itself.

I thought of chiming in here but MaxJohnson is handling it very well.......

Damn, I guess I'll say one thing.......when your nose is pointing to the sky it makes little difference what anti-dive you have in the front, think about it.